Method of coating and working metal



July 7, 1959 F. x. MCCAWLEY METHOD OF COATING AND WORKING METAL FiledJune 28, 1957 mufimnw 20E 3: N w m o. N.

QmPOuhOmaZD 7 INVENTOR .FRANK x. MSCAWLEY BY w ATTORNEY inertatmosphere.

United States Patent METHOD OF COATING AND WORKING METAL Frank X.McCawley, Cheverly, Md., assignor to Chicago Development Corporation,Riverdale, Md., a corporation of Delaware Application June 28,1957,Serial No. 668,771

' 1 Claim. ores-424 "electrolytic process. For this purpose, I provide amolten bath of strontium, barium, sodium, potassium, lithium or calciumchloride. The bath may contain a mixture of these chlorides. I prefer amixture of alkaline earth and alkali chlorides. I particularly prefer touse a bath containing 65% SrCl 35% NaCl, because such a bath is moltenat relatively low temperatures and 810% titanium can be dissolved in itas lower chlorides together with one of the alkali or alkaline earthmetals.

When the metal to be coated with TiC is coated with graphite and made acathode in such a bath, a layer of titanium carbide is formed on itssurface. The thickness of this layer depends on the thickness of theadherent graphite layer Which can be applied. In most cases, this is onthe order of 1 mil.

The extent of protection afforded for a titanium surface during hotworking is illustrated in the sole figure which shows the oxygenpenetration for unprotected titanium, for titanium protected by a saltlayer and for titanium protected by a layer of titanium carbide.

I have used other procedures for producing a layer of titanium carbideon titanium such as heating to a high temperature in argon containing asmall percentage of hydrocarbon gas. I have found, however, thattitanium carbide layers produced in this manner are less adherent andprotective.

Having now described my invention in its more general terms, I willillustrate it by examples.

Example I I take an ingot 4" x 4" x of titanium-vanadium alloycontaining 4% V, 01% oxygen, balance substantially titanium. I splitthis lengthwise to obtain two identical portions each 2" x 4" x 10". Icoat one of these with graphite and make it a cathode in a cell having aparticulate titanium anode contained in an annular perforate iron basketand the cathode disposed in the center of the cell surrounded by theperforate basket. The cell is provided With an inert atmosphere andmeans for raising the cathode out of the bath and cooling it in an Thecell bath consisted of 65% strontium chloride 35% sodium chloride inwhich was dissolved 8% titanium as chloride, average valence 2.4 and 3%alkalinous metal calculated as sodium. A di- 2,893,115 Patented July 7,1959 rect current of amperes was passed for minutes at 750 C.

After cooling in an inert atmosphere, the portion of the ingot withadhering salt, fine titanium crystals and titanium carbide layer isplaced in a furnace at 900 C. along with the untreated portion. Heatingis continued for 1 hour and both pieces are hot rolled to A" thicknesswithout reheating. They are then reheated for 15 minutes and hot rolledto A" thickness. Both pieces are then scalped to remove 4 mils of theoriginal metal on both sides. The piece protected by the platingoperation then analyzed .014 oxygen and the other piece .071

oxygen. Example I! I take a bar Mt" x 12" x 3' steel and treat it in thesame manner as the titanium alloy ingot in Example I to produce acoating of titanium carbide on the bar. I hot roll this bar at 750 C. to40 gauge strip. The resulting strip has a coating of titanium carbidewhich protects the steel from surface contamination. I take severalportions of the sheet and galvanize it by hot dripping. The adherence ofthe zinc is good and the brittle layer of iron zinc alloy common in hotgalvanizing is absent.

Example 111 I proceed as in Example I except that the cell bath is NaClin which is dissolved 4.5% titanium as chloride, average valence 2.4 and.3% sodium. The bath temperature is 850 C. The metal treated is highlypure zirconium. The results are identical with those of Example I.

Example IV I proceed as in Example I except that I use a cell bath ofKCl 10% BaCl in which is dissolved 2% titanium as chloride, valence 2.15and 2.5% alkalinous metal (calculated as K). The metal to be treated isa zirconium alloy containing .2% iron. The results as to oxygenabsorption on hot rolling are the same as in Example I.

Example V I proceed as in Example I except that the cell bath is 50%CaCl 50% LiCl and the metal to be treated is pure titanium. Thetemperature of the cell bath is 800 C. The results obtained areidentical with those in Example I.

Example VI I take a strip 4" thick of pure titanium containing .0l%oxygen and substantially no other impurities. I heat this strip in amixture of CH, and TiCL, at 800 C. whereby to coat it with TiC. I butroll the so-coated strip at 850 C. to reduce it to one-half itsthickness. I scalp .004 inch from each side. The resulting stripanalyzes .02% oxygen.

Example VII In this example I apply the procedure of my invention to theprotection of titanium-aluminum alloys during hot working. Such alloysof usual purity containing 10% aluminum have been found to break up whenhot rolled at 1650 F. I have found that this is due to very rapid oxygenabsorption. In this example I make an ingot of aluminum-titanium alloycontaining 10% aluminum, .02% oxygen, and substantially no otherimpurity. I cast this ingot by rubbing with flake graphite and thenprovide a further carbon coating by exposing the ingot to a smokyacetylene flame. I make this ingot a cathode in a bath consisting ofcalcium chloride having dissolved therein 10% titanium chloride, averagevalence 2.4, and 3% metallic calcium, the anode is particulate titanium.I employ a cathode current density of amperes/sq.

ft. for 15 minutes. A titanium carbide layer is formed on the ingotwhich layer is covered with salt and finely divided titanium. The soprotected ingot is heated to 165.0 Ftvin air. and hot rolled. The hotrolling proceeds smoothly, and an analysis of the hot rolled baraftenremoving. .005. inch from the surface shows 10,1%- aluminum,f .025%oxygen, balance substantially titanium.

whatisiclaimed-is: 5 The method of. fabricating a metalselected from thegroup consisting of titanium, and zirconium, and alloys consistingprincipally bf these metals which consists in coating said metal withcarbon and making it a cathode in anelectrolyticcellshaving a fusedelectrolyte of at least onechloride; selected from the group consistingof calciurn, strontium, barium, sodium, potassium and lithium chloridesand dissolved therein 140% titanium aslower chlorides and .1-5 of ametal corresponding to the chlorides of the fused electrolyte, andpassing a direct current from a particulate titanium anode to saidcathode whereby to form a coating on the cathode surface and thenfabricating the metal by subjecting it to working at temperatures from750-900 C., whereby to limit oxygen absorption to .02'% when a surfacelayer about 5 mils: thick is removed.

References Cited in the file of this patent UNITED STATES PATENTS

